This invention relates to a plastic identifying apparatus and a method thereof to identified by what type of plastic the object to be identified is formed.
In the recent years, the recycling of plastic products (especially PET bottles) has been proceeded. For efficient recycling, it is necessary to identify and sort plastic products depending on the type of their material, and it is being a theme how to conduct the identification of plastic products.
As a conventional plastic identifying apparatus using light, there is one in which near-infrared ray is irradiated to a plastic product while continuously changing the wavelength in the wavelength region of 1 to 2.5 xcexcm, and the differential spectrum of its absorption spectrum is analyzed to identify the type of plastic forming the plastic product.
However, since in this conventional identifying apparatus it is necessary to irradiate near-infrared ray to plastic products while continuously changing the wavelength in the wavelength region of 1 to 2.5 xcexcm, there is the problem that the optical system is complicated. Further, such a complicated processing of finding the differential spectrum is also needed in a signal processing after light receiving, and there are the problem that the apparatus construction and signal processing are complicated, and the problem that identification is time-consuming.
In addition, as regards the light source in this case, an incandescent lamp and mercury lamp are usually employed as one which emits near-infrared ray having a wavelength region of 1 to 2.5 xcexcm. Hence, there is the problem due to the lifetime of the light source that its maintenance is laborious and the apparatus cost is increased as a whole.
In this conventional technique, there is a method in which no scanning of wavelength on the light source side is performed and an irradiation light having a wide wavelength region is irradiated from a light source and, when receiving the light, a wavelength selection is performed by using a spectral device such as grating. However, the problem of the light source lifetime is not solved, in addition to the fact that the cost is increased because the spectral device itself is extremely expensive.
It is a first object of this invention to provide a plastic identifying apparatus and a method thereof which enable to simplify the apparatus structure and signal processing and also attain a rapid identifying processing.
It is a second object of this invention to provide a plastic identifying apparatus and a method thereof, taking less time for maintenance.
Accordingly, in order to attain the above objects, this invention provides a plastic identifying apparatus (1, 21, 31, 41, 51) to identify by what type of plastic in predetermined plural types an object made of plastic to be identified (4) is formed, characterized by comprising a light source (2, 3, 3a, 3b) irradiating to said object to be identified a detecting light (L2, L2a, L2b) of which wavelength is in an absorption wavelength band to increase the light absorptance of at least one type of plastic in said plural types, and a reference light (L1) of which wavelength is different from said wavelength of said detecting light; a light receiving means (5, 5a, 5b, 5c) receiving a transmitted light or reflected light of said reference light and said detecting light from said object to be identified, and outputting a reference value expressing the quantity of light received of said reference light and a detecting value expressing the quantity of light received of said detecting light; and an identifying means (7) computing a proportion of or difference between said reference value and said detecting value, and identifying, based on the computed value, by what type of plastic in said plural types said object to be identified is formed.
Also, in order to attain the above objects, this invention provides a plastic identifying method of identifying by what type of plastic in predetermined plural types an object made of plastic to be identified (4) is formed, characterized by comprising the steps of: a light irradiating step of irradiating to said object to be identified, by a predetermined light source, a detecting light (L2, L2a, L2b) of which wavelength is in an absorption wavelength band to increase the light absorptance of at least one type of plastic in said plural types, and a reference light (L1) of which wavelength is different from said wavelength of said detecting light; a light receiving step of receiving by a predetermined light receiving means (5, 5a, 5b, 5c) a transmitted light or reflected light of said reference light and said detecting light from said object to be identified, and outputting to said light receiving means a reference value expressing the quantity of light received of said reference light and a detecting value expressing the quantity of light received of said detecting light; and an identifying step of computing a proportion of or difference between said reference value and said detecting value, and identifying, based on the computed value, by what type of plastic in said plural types said object to be identified is formed.
With this construction, it is unnecessary to scan the irradiation light in a predetermined wavelength region, as has been conventional, so that the apparatus construction such as of optical system and the signal processing after light receiving can be simplified, and a rapid identification can be attained.
Further, it is so arranged as to compute a proportion of or difference between a reference value expressing the quantity of light received of a reference light and a detecting value expressing the quantity of light received of a detecting light, and then perform identification based on the computed value. Therefore, the identification can be conducted by removing the unnecessary variable factor that varies depending on factors other than the type of plastic, for example, the shape of the object to be identified or the surface state such as dirt and damage. This leads to accurate identification.
Furthermore, in the case that identification is conducted by using the proportion of a reference value and a detecting value, when obtaining the proportion, the magnitude of the detecting value is standardized by the reference value. Therefore, there is the advantage that without specially standardizing the emission intensity and the like of a reference light and detecting light of a light source, the identification can be conducted irrespective of their setting conditions.